1. Technical Field
This disclosure relates in general to step-down DC-DC switching converters and in particular to self powering techniques of the control circuits of the converter through an internal linear voltage regulator that is connected to the output voltage node of the converter, disconnecting it from the input voltage node thereof, in order to reduce power absorption.
2. Description of the Related Art
By using the output voltage of the converter itself for supplying the controller of a power switch adapted to intermittently transfer electrical power from the input node to the output node and an external electrical load, power consumption within the controller may be reduced by a factor equal to the ratio between the output voltage and the input voltage.
Possible solutions have been sought and circuital embodiments proposed for exploiting this opportunity when work conditions of the converter may consent it, but they have shortcomings of non-fully optimal management of the energy saving and/or of being applicable only to restricted types of applications.
The document U.S. Pat. No. 5,528,132-A describes a method and related circuit wherein an internal voltage regulator of the DC-DC converter is coupled to the output voltage node when the output voltage becomes greater than the nominal (design) voltage of the linear regulator. The proposed circuit architecture is depicted in FIG. 1. Clearly, the output voltage values must be compatible with the admissible maximum supply voltage of the internal circuitry on the chip. Wherever a broader variability of the output voltage (beyond said compatibility limit) is desired, this solution is inapplicable because of the risk of destroying the chip if the output voltage should overcome said safe operation voltage of the control circuit components.
The published patent application US2006001409-A1, describes a circuit the architecture of which is depicted in FIG. 2. The linear voltage regulator internal to the DC-DC converter has two distinct output stages, one connected to the input voltage node of the converter and the other to the output voltage node, which are selectively driven by the linear regulator depending on whether the output voltage is lower or greater than a reference voltage. Though compatible with any level of output voltage of the converter, the absorption of the linear regulator persists in every functioning condition.